The SSODB has been removed from version 5.5 onwards but as the upgrades happen from older vCenter versions, it can get carried along. This DB has been dropped in the later versions but can be carried along as an orphaned object. Dropping this manually will not cause any issues as this is not used anywhere.
Resolution
Please take a snapshot of the vCenter VM before proceeding with below steps. If there are multiple vCenters in Enhanced Linked Mode, then power off all the VC nodes and take a offline snapshot.